Supercritical carbon dioxide as a green solvent for processing polymer melts:Processing aspects and applications

Supercritical carbon dioxide (CO(2)) is Well established for use as a processing solvent in polymer applications such as polymer modification, formation of polymer composites, polymer blending, microcellular foaming, particle production and polymerization. Its gas-like diffusivity and liquid-like density in the supercritical phase allow replacing conventional, often noxious, solvents with supercritical CO(2). Though only a few polymers are soluble in supercritical CO(2), it is quite soluble in many molten polymers. CO(2) dissolution in a polymer has been interpreted physically but FT-IR studies lead to an explanation in terms of weak interactions between basic and acidic sites. Various experimental methods and equations of state are available to measure or predict the solubility of CO(2). Dissolved CO(2) causes a considerable reduction in the viscosity of molten polymer, a very important property for the applications stated above. CO(2) mainly acts as a plasticizer or solvent when contacted with a polymer. Gas solubility and viscosity reduction can be predicted theoretically from pure-component properties. In this review, experimental and theoretical studies of solubility and viscosity of several polymer melts are discussed in detail. Detailed attention is also given to recently reported applications along with aspects related to polymer processing. (c) 2005 Elsevier Ltd. All rights reserved

Solubilities of sub- and supercritical carbon dioxide in polyester resins

In supercritical carbon dioxide (CO2) assisted polymer processes the solubility of CO2 in a polymer plays a vital role. The higher the amount of CO2 dissolved in a polymer the higher is the viscosity reduction of the polymer. Solubilities Of CO2 in polyester resins based on propoxylated bisphenol (PPB) and ethoxylated bisphenol (PEB) have been measured using a magnetic suspension balance at temperatures ranging from 333 to 420 K and pressures up to 30 MPa. An optical cell has been used to independently determine the swelling of the polymers, which has been incorporated in the buoyancy correction. In both polyester resins, the solubility of CO, increases with increasing pressure and decreasing temperature as a result of variations in CO, density. The experimental solubility has been correlated to the Sanchez-Lacombe equation of state.</p

Polymer melt micronisation using supercritical carbon dioxide as processing

Plastic is een materiaal dat in de industrie vooral populair is omdat je het met het grootste gemak in alle mogelijke vormen kunt gieten. Om er kleine, gelijkvormige bolletjes van te maken is echter een kunst apart. De kunststof polyester wordt in deze vorm gebruikt als poeder voor toner. De farmaceutische industrie gebruikt bolletjes van polyethyleenglycol om geneesmiddelen in te kapselen die gecontroleerd moeten worden gedoceerd. In een nieuwe methode voor het maken van dergelijke deeltjes in de grootte van nanometers tot micrometers wordt CO2-gas gebruikt ter vervanging van milieu-onvriendelijke chemische oplosmiddelen. Sameer Nalawade deed onderzoek naar het optimaliseren van deze productiemethode. Hij maakte daarbij gebruik van een extruder (schroefvormige vermaler) en een mengapparaat met spuitmond. Behalve voor het milieu biedt de methode ook veel voordelen in economisch en technisch opzicht.

The FT-IR studies of the interactions of CO2 and polymers having different chain groups

A Fourier transform-infrared spectroscopy (FT-IR) set up has been successfully modified in order to characterize different polymeric materials under sub- and supercritical CO2 conditions. Polymers used in this study are polyesters (P120 and P130), poly(ethylene glycol) (PEG) and polyphenylene oxide (PPO). Analysis of the corresponding spectra shows evidences of weak interaction (Lewis acid–base) between CO2 and polymers. In particular, shifts to higher wavelengths of the maximum absorption of chain groups of the polymer and the modification of the absorption band of CO2 represent a qualitative evidence of such interactions. Analysis of CO2 absorption bands allowed ranking of the polymeric materials according to interaction strength with CO2. In general, polymers with ether group display higher interaction strength than polyesters. The effect of the dissolved CO2 on the depression of the melting point, Tm or the glass transition temperature, Tg can also be studied using the FT-IR depending on the enhancement in the free volume. The shape of the spectrum in PEG, unlike the other polymers, was completely modified above the critical pressure (7.38MPa).

Batch production of micron size particles from poly(ethylene glycol) using supercritical CO2 as a processing solvent

The major advantage of using supercritical carbon dioxide (CO2) as a solvent in polymer processing is an enhancement in the free volume of a polymer due to dissolved CO2, which causes a considerable reduction in the viscosity. This allows spraying the polymer melt at low temperatures to produce micron size particles. We have used supercritical CO2 as a solvent for the generation of particles from poly(ethylene glycol) (PEG) of different molecular weights. Since PEG is a hydrophilic compound, it is a most commonly used polymer for encapsulating a drug. PEG particles with different properties may allow keeping a good control over the release of the drug. It has been possible to produce particles with different size, size distribution, porosity and shape by varying various process parameters such as molecular weight, temperature, pressure and nozzle diameter. A flow and a solidification model have been applied in order to have a theoretical insight into the role of different parameters.

Supercritical carbon dioxide as a green solvent for processing polymer melts: Processing aspects and applications

Supercritical carbon dioxide (CO2) is well established for use as a processing solvent in polymer applications such as polymer modification, formation of polymer composites, polymer blending, microcellular foaming, particle production and polymerization. Its gas-like diffusivity and liquid-like density in the supercritical phase allow replacing conventional, often noxious, solvents with supercritical CO2. Though only a few polymers are soluble in supercritical CO2, it is quite soluble in many molten polymers. CO2 dissolution in a polymer has been interpreted physically but FT-IR studies lead to an explanation in terms of weak interactions between basic and acidic sites. Various experimental methods and equations of state are available to measure or predict the solubility of CO2. Dissolved CO2 causes a considerable reduction in the viscosity of molten polymer, a very important property for the applications stated above. CO2 mainly acts as a plasticizer or solvent when contacted with a polymer. Gas solubility and viscosity reduction can be predicted theoretically from pure-component properties. In this review, experimental and theoretical studies of solubility and viscosity of several polymer melts are discussed in detail. Detailed attention is also given to recently reported applications along with aspects related to polymer processing.

Prediction of the viscosity reduction due to dissolved CO2 of and an elementary approach in the supercritical CO2 assisted continuous particle production of a polyester resin

The dissolution of CO2 in a polymer causes plasticization of the polymer and hence, its viscosity is reduced. A model based on the free volume theory has been used for a polyester resin, which shows a considerable reduction in the viscosity due to dissolved CO2. Therefore, supercritical CO2 has been used as a processing solvent in the continuous production of micron size particles of the resin. Despite the viscosity reduction caused by the dissolved CO2, an excess quantity of CO2 with respect to its solubility limit has been used for micronisation of the polymer due to its high viscosity. The mixing of CO2 and the polymer has not been possible in an extruder at high gas to polymer mass ratios and consequently, a simplified Kenics type static mixer has been used for the mixing purpose. In this study, the effect of various parameters such as temperature, pressure, nozzle diameter and gas to polymer mass ratio on the particle morphology and size has been studied. The experimental results manifest the technological as well as the theoretical insight into the particles production from a high viscosity material.

Solubilities of Sub- and Supercritical Carbon Dioxide in Polyester Resins

In supercritical carbon dioxide (CO2) assisted polymer processes the solubility of CO2 in a polymer plays a vital role. The higher the amount of CO2 dissolved in a polymer the higher is the viscosity reduction of the polymer. Solubilities of CO2 in polyester resins based on propoxylated bisphenol (PPB) and ethoxylated bisphenol (PEB) have been measured using a magnetic suspension balance at temperatures ranging from 333 to 420 K and pressures up to 30 MPa. An optical cell has been used to independently determine the swelling of the polymers, which has been incorporated in the buoyancy correction. In both polyester resins, the solubility of CO2 increases with increasing pressure and decreasing temperature as a result of variations in CO2 density. The experimental solubility has been correlated to the Sanchez–Lacombe equation of state.

Influence of electron beam irradiation on physicochemical properties of poly(trimethylene carbonate)

Electron beam (EB) irradiation of poly(trimethylene carbonate) (PTMC), an amorphous, biodegradable polymer used in the field of biomaterials, results in predominant cross-linking and finally in the formation of gel fraction, thus enabling modification of physicochemical properties of this material without significant changes in its chemical structure. PTMC films (M(w): 167-553 kg mol(-1)) were irradiated with different doses using an electron accelerator. Irradiation with a standard sterilization dose of 25 kGy caused neither significant changes in the chemical composition of the polymer nor significant deterioration of its mechanical properties. Changes in viscosity-, number-, weight-, and z-average molecular weights of PTMC for doses lower than the gelation dose (D(g)) as well as gel sol analysis and swelling tests for doses above D(g) indicate domination of cross-linking over degradation. EB irradiation can be considered as an effective tool for increasing the average molecular weight of PTMC and sterilization of PTMC-based biomaterials. (C) 2011 Elsevier Ltd. All rights reserved